1. Field of the Invention
The present invention relates generally to compression testing machines and, more particularly, to a new and unique compression testing machine for indicating the playing condition of a tennis ball or the like.
2. Description of the Prior Art
The playing condition of a tennis ball or the like is very important to the players. Despite stringent efforts to properly inflate the balls during manufacturing to predetermine degrees of pressure, followed by careful testing and pressure packaging, tennis balls and the like frequently do not have the uniform bounce and other play characteristics required for play, particularly professional play.
The primary characteristic which is necessary to good playing condition is compressibility. Normally, the only way for a player to determine the compressibility of the balls is to squeeze them manually or bounce them. These are not sufficiently accurate methods for gauging the playing condition of the tennis ball. Accordingly, competitive players customarily disregard balls after relatively short intervals of play and open new balls to insure uniform performance during play.
Under American Tennis Association (ATA) rules, a tennis ball should have a rebound of more than 53 inches and less than 58 inches when dropped 100 inches upon a concrete base. Specifically, the ball shall have a forward deformation of more than 0.220 inches and less than 0.290 inches and a return deformation of more than 0.350 inches and less than 0.425 inches at a 18 lb. load.
Under the ATA rules, all deformation tests conducted under Rule 3 shall use a machine designed by Percy Stevens and patented in Great Britain under Patent No. 230,250, the entire specification of which is hereby incorporated by reference. Deformation testing is conducted by placing the ball on the Stevens machine so that neither platen of machine is in contact with the cover seam. The contact weight is then applied and the dials are set to zero. A test weight equivalent to 18 lbs. is placed on the beam and pressure is applied by turning the wheel at uniform speed so that the pointer on the machine is level with the mark to balance the pressure placed on the beam. The amount of deformation caused to the ball is its forward deformation value. It is this value that is the most critical to indicating the condition of the tennis ball. Clearly, such measurements are too complicated and the Stevens device is too cumbersome to be used except for as part of manufacturing quality control and for professional tournament play.
U.S. Pat. No. 4,590,808 issued to Lightfoot discloses a device and method for determining the tension factor of grids such as tennis rackets and the like. The device includes a frame having a fixed predetermined test area including a mechanism for relating two measurement components, a deflection component and a force component; an element for applying a first measurement component to the grid test area; an element for sensing the other component resulting from the application of the first component; and means for determining from the two components a tension factor in the strings forming the grid. The apparatus also includes a mechanism and method for determining the compressibility of balls such as tennis balls.
U.S. Pat. No. 4,313,289 issued to Birdsong discloses a method for manufacturing a tennis ball, racket ball or other gas-filled ball by inflating the ball with air or gas to such a degree that the ball will precisely balance a given force on the ball producing a given deflection on the ball.
U.S. Pat. No. 3,665,757 issued to Hoag discloses a gauge for checking the concentricity and the compression of a golf ball having a lever for moving a first anvil a given distance against the ball, thereby forcing the ball to move against a second anvil which registers the ball compression against a helical spring on a dial gauge. U.S. Pat. No. 2,278,416 issued to Atti discloses a similar type device.
Finally, U.S. Pat. No. 2,703,492 issued to Brissette and U.S. Pat. No. 2,626,522 issued to Brown are examples of devices for measuring the modulus of compression of rubber-like materials.
As can be seen from a review of the these references, none of the prior art devices provide a simple, economical and reliable means for measuring the condition of a tennis ball in a device which is portable and which can be used by a player on the court to provide a "go-no go" indication of the condition of the game ball. Thus, there remains a need for a new and improved tennis ball tester which is simple and economical to operate and which provides a reliable indication of the condition of the tennis ball.